The present invention relates to a roll control system for an automotive vehicle, and more specifically relates to a vehicle roll control system of the vehicle height adjustment type which is particularly adapted for preventing suspension overshoot.
The present invention has been described in Japanese Patent Applications Ser. Nos. 60-235655 (1985) 60-235656 (1985), and 60-235657 (1985), all three of them filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the texts of said Japanese Patent Applications and the claims and the drawings thereof; copies are appended to the present application.
Further, the present inventors wish hereby to attract the attention of the examining authorities to copending Patent Applications Ser. Nos. 921,138, 921,251, 921,450, and 921,451, which may be considered to be material to the examination of the present patent application.
In general, in the operational conditions where a vehicle such as an automobile turns at a speed not less than a particular determinate turning speed value, the body of the vehicle experiences rolling, i.e. the vehicle body inclines in the radially outward direction and tips towards the wheels on its radially outward edge, and this rolling can easily result in deterioration of the drivability of the vehicle.
In order to cope with the above problem, in the case where a vehicle is fitted with a suspension system which comprises shock absorber means and/or spring means whose damping effect and/or whose spring constant can be varied, as for example by an electronic control device therefor, it might be considered, during such a turn, to increase the damping effect of those of the shock absorber means which are fitted to said wheels on the radially outward edge of the vehicle, and/or to increase the spring constant of those of the spring means which are fitted to said wheels on the radially outward edge of the vehicle. Such a concept is outlined in Japanese Patent Laying Open Publication Ser. No. 59-120509 (1984) and in Japanese Patent Application Ser. No. Sho 59-172416 (1984), neither of which is it intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law; and reference should also be made to Japanese Utility Model Laying Open Publication Ser. No. 59-35105 (1984), Japanese Patent Laying Open Publication Ser. No. 53-26021 (1978), Japanese Patent Laying Open Publication Ser. No. 58-167210 (1983), and Japanese Utility Model Laying Open Publication Ser. No. 56-147107 (1981), again none of which is it intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law. However, with this concept, merely the suspension of the vehicle on the outer edge side thereof with respect to the turn is hardened, and thus the rolling of the vehicle body may be somewhat attenuated as compared with the case when such suspension hardening is not performed, but the rolling of the vehicle body cannot necessarily be adequately prevented. Accordingly, such a concept does not really resolve the problem.
Further, in the case where a vehicle is fitted with a vehicle height adjustment system comprising: a plurality of actuators which are provided for resiliently suspending the vehicle wheels from its body and are adapted to increase or decrease vehicle height at locations corresponding to the associated vehicle wheels as respective results of supplying or discharging working fluid to or from variable volume working fluid chambers of said actuators (such actuators are typically controlled by duty ratio control); a plurality of working fluid supplying and discharging means which are provided corresponding to the actuators and which serve to supply or discharge the working fluid to or from said actuators; a vehicle height detecting means for sensing vehicle height; and a control means for controlling the working fluid supplying and discharging means based upon the data sensed by the vehicle height detecting means in order to adjust the vehicle height to a predetermined vehicle height, (as proposed, for example, in the specifications of Japanese Patent Laying Open Publication Ser. No. Sho 60-85005 (1985) and Japanese Patent Laying Open Publication Ser. No. Sho 60-235654 (1985), both of which were filed by an applicant the same as one of the applicants or one of the assignees or one of the entities owed duty of assignment of the present application and which it is similarly not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, it might be conceived of to actively achieve vehicle height adjustment during running of the vehicle around a curve, in order to thereby prevent completely the vehicle body from rolling, by controlling the working fluid supplying and discharging means based upon the differences between the actual vehicle heights and reference vehicle heights.
In a vehicle which was equipped with such a vehicle height adjustment system as described above, however, it would be necessary rapidly to supply or drain hydraulic fluid in quantity to the hydraulic fluid chamber of each actuator when the vehicle is travelling around a curve, as compared with the amount of hydraulic fluid which is required to be supplied or drained to the hydraulic fluid chamber of each actuator in the case that the vehicle is stationary or is substantially travelling in a straight line. Therefore, when using such a system for wheel height adjustment in such a manner to restrict the vehicle roll while travelling around a curve, it would become quite likely that the wheel height adjustment might come to exceed the standard wheel height and be excessive, causing so called overshoot, and, particularly in the case of a hydro-pneumatic type of suspension in which air springs were coupled to the hydraulic actuating chambers, because the internal pressure of the air springs would increase or would decrease excessively, after roll control of the vehicle was completed, the rise or fall of one side or the other of the vehicle might tend to fluctuate repeatedly until the pressure within the hydraulic actuation chamber or the pressure within the air spring reached its equilibrium pressure, and as a result the wheel height would repeatedly rise and fall beyond the standard desired wheel height. This could present a troublesome problem, and accordingly the viability of such an approach as described above is compromised.